A magnetic heat pump apparatus is known in the art, for example, as disclosed in French Patent Publication No. 2943406, according to which magnetocaloric element of magnetic working material is magnetically and periodically operated or released from its magnetic operation, cooling fluid is alternately moved to a high-temperature chamber and a low-temperature chamber (which are provided at both sides of the magnetocaloric element) so that the cooling fluid passes through the magnetocaloric element in synchronism with a magnetic-field applying stage or a magnetic-field releasing stage of the magnetocaloric element, and transfer of heat is thereby carried out. According to such a prior art, flow direction of the cooling fluid passing through the magnetocaloric element is reversed in the magnetic-field applying stage and the magnetic-field releasing stage, so that the cooling fluid continuously flows in a reciprocating manner.
The above prior art does not disclose anything about a relationship between an increase-decrease rate of magnetic field to be applied to the magnetocaloric element and a flow speed of the cooling fluid. It may be a problem that an operating condition of the magnetic heat pump apparatus differs from Carnot cycle (which is one of ideal heat cycles) and thereby sufficiently high operation efficiency cannot be realized.